The MEASURE Study - A Phase 3 Study of MDX 1400 mg Daily Compared With Placebo in Adults With ADHD

Inclusion Criteria: 1. Subject is a man or a non-pregnant, non-lactating woman 18 to 55 years of age, inclusive, at the Screening visit. 2. Subject has a diagnosis of ADHD based on criteria in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM5) as assessed by the Adult ADHD Clinician Diagnostic Scale, (ACDS Version 1.2) modified for DSM-IV and DSM5 diagnoses; a diagnosis of ADHD not otherwise specified is unacceptable. 3. Male and Female subjects of childbearing potential must agree to use an effective contraceptive throughout the study 4. Subject is able to attend the clinic regularly and reliably. 5. Subject is able to swallow tablets and capsules. 6. Subject is able to understand, read, write, and speak the local language fluently to complete the study-related materials. 7. Subject is able to understand and sign an informed consent form to participate in the study. Exclusion criteria 1. Subject has any current major psychiatric condition (e.g., schizophrenia, bipolar or personality disorder) or autism spectrum disorder. 2. Subject has any clinically significant or unstable medical or surgical condition that may preclude safe and complete study participation. 3. Subject has used an investigational medication/treatment or was enrolled in another clinical trial in the 30 days before the Screening visit. 4. Subject has used any medication or food supplement that the investigator or the medical monitor consider unacceptable during the 14-day period before the Baseline visit. 5. Subject's alcohol and caffeine intake will be assessed. 6. Subject has current suicidality, defined as active ideation, intent or plan, or any significant lifetime suicidal behavior (actual attempt, aborted attempt, interrupted attempt, or act or preparation towards imminently making a suicide attempt). Subjects exhibiting history (within previous 12 months) of non-suicidal self-injurious behavior will be excluded. 7. Subject has taken any prescription or non-prescription medication for ADHD during the 14 days (or 21 days for atomoxetine) before the Baseline visit. Subjects will not be allowed to take any other medications for ADHD besides the study medication (when prescribed) after the washout period and for the duration of the study, up to and including the safety Follow-up visit. (Other ADHD medications should NOT be prescribed to subjects before completion of the Follow-up visit or Early Termination Visit). 8. Subject is significantly visually impaired to an extent that is not able to be corrected by prescription glasses or contact lenses. 9. Subject is closely related to the sponsor, investigator, or study staff. Eligibility of subjects with any relationship to the sponsor, investigator, or study staff will be discussed with the medical monitor before study entry, and the medical monitor will decide on the eligibility of these cases. 10. Subject has previously been enrolled in an MDX clinical trial. 11. Subject lives in the same household as another subject in this clinical trial or in another on-going trial with MDX. Subject lives in the same household as someone who has previously participated in a trial with MDX. 12. Subject has any condition that, in the principal investigator's opinion, would place the subject at risk or influence the conduct of the study or interpretation of results, including (but not limited to) abnormally low intellectual capacity as judged by the investigator. 13. Subject cannot fully comprehend the implications of the protocol, cannot comply with its requirements, or is incapable of following the study schedule for any reason. 14. Subject is pregnant, lactating, or using an inadequate contraceptive method. Complete entry criteria will be reviewed and evaluated individually by a protocol trained delegate.